3,5-ditert.butyl-4-hydroxybenzaldehyde is a compound which is useful as a chemical intermediate for manufacture of pesticides of the benzylidenemalononitrile type. There is a need for an uncomplicated process for manufacturing this compound in good yields from inexpensive and readily available starting materials. An attractive starting material for manufacture of the desired product is 2,6-ditert.butylphenol which is a readily available article of commerce. Known procedures for formylation of this compound are too complicated, give only mediocre yields or employ expensive reagents. By way of illustration there has been described by W. Smith [J. Org. Chem. v. 37, 3972-3 (1972)] the reaction of 2,6-ditert.butylphenol with an equimolar quantity of hexamethylenetetramine in trifluoroacetic acid reaction medium. The yield obtained was 60 percent. Hexamethylenetetramine has been employed in the Duff reaction to effect formylation of phenols, but yields are generally low [Chemical Reviews v. 38 p. 230 (1946)].